1. Technical Field
The present invention relates to a network interfacing and more particularly, to methods and systems for efficiently transmitting data packets on a high speed packet switched network, such as a gigabit Ethernet network.
2. Description of the Related Art
Local area networks use a network cable or other media to link stations on the network. Each local area network architecture uses a media access control (MAC) enabling a network interface card at each station to share access to the media.
The Ethernet protocol ISO/IEC 8802-3 (ANSI/IEEE Std. 802.3, 1993 edition) defines a half-duplex media access mechanism that permits all stations to access the network channel with equality. Traffic is not distinguished or prioritized over the medium. Each station includes an Ethernet interface card that uses carrier-sense multiple-access with collision detection (CSMA/CD) to listen for traffic on the media. A station having data to send will attempt to access the channel by waiting a predetermined time after the deassertion of a receive carrier on the media, known as the interpacket gap (IPG) interval.
A full duplex environment has been proposed for Ethernet networks, referred to as IEEE 802.3x, Full Duplex with Flow Control-Working Draft (0.3). The full duplex environment provides a two-way, point-to-point communication link between two network stations using a switched hub. Hence, two stations can simultaneously transmit and receive Ethernet data packets between each other without collision.
The IEEE 802.3z Task Force is currently defining standards for the operation of a shared (i.e., half-duplex) and full-duplex gigabit Ethernet. Two modifications have been proposed to the existing Ethernet (802.3) protocol for implementation of shared gigabit Ethernet networks, namely extending the carrier by increasing the slot time to 512 bytes (4096 bits) without increasing the minimum frame length, and providing frame bursting in which a station sends several frames separated by the extend carrier symbols in a single burst.
The proposed frame bursting for gigabit Ethernet operates by a station operating according to the conventional CSMA/CD protocol when attempting to transmit the first packet. A burst timer is started at the beginning of the transmission of the first frame. If the first packet transmission is successful, the station can send an additional frame provided the following two conditions hold: (1) the burst timer has not expired, and (2) the station has another frame to send. This step is repeated until the burst timer expires or the station has no frame to send, whichever occurs first. The carrier sense is held high by the transmitting station during the entire burst. The IEEE 802.3z Task Force is currently contemplating setting the burst timer to limit the burst duration to a maximum duration of 65536 bits.
If a collision occurs during transmission of the first frame on the gigabit Ethernet media, the station follows the normal CSMA/CD operation sequence of jam, abort, and backoff collision mediation. A new burst of frames can occur only when a station has sent the first packet successfully.
Prior efforts at rate control of a shared medium typically involved use of a central management entity. For example, a token ring network passes a token in a sequential manner to network stations. A station that acquires the token has the right to transmit on the network. Upon completion of the transmission, the token is passed on to the next station. The passing of the token, however, uses up bandwidth on the media. Bandwidth is also wasted if the token is received and then passed by a station that has no data to transmit. Hence, the token ring network limits network throughput because an individual station cannot transmit data until it receives the token, regardless of whether any other station has any data to send.
Another network arrangement specified by IEEE 802.12-1995, "Demand Priority Access Method, Physical Layer and Repeater Specification for 100Mb/s Operation," also known as the VG ANYLAN network, uses a centralized hub to arbitrate among the requests from network stations. The hub grants access to the stations in a round robin fashion. However, the VG ANYLAN network still requires control by a central hub.
Other proposals suggest the user of a central management entity to assign a slot number to each station on the network, where a station transmits only when a current slot number is equal to the station slot number. Such proposals also require a centralized management entity to manage the network.